Clear Channel Assessment (CCA) is a carrier sense mechanism in wireless local area network (WLAN) or Wi-Fi which can be used to determine if a radio (e.g., a transmitter) can use a wireless channel to transmit wireless signals. CCA is defined in IEEE 802.11-2007 standards as part of the Physical Medium Dependent (PMD) and Physical Layer Convergence Protocol (PLCP) layer. CCA has two related functions: carrier sense (CCA-CS) and energy detect (CCA-ED).
In CCA-CS, a receiver detects and decodes a WiFi preamble in a received frame. The duration for which the channel will be used is typically put in the PLCP header field in the received frame. The channel is then assumed to be busy until the end of that duration.
In CCA-ED, the receiver detects non-WiFi energy in the channel (e.g., interference from microwaves or natural sources) as well as data transmission from other interfering WiFi devices. The receiver determines if the total energy in the channel is less than a predefined energy detect (ED) threshold (typically defined as 20 dB above the minimum receiver sensitivity of the physical layer (PHY)). If so, the channel is deemed busy and unusable to the device. However, if the energy is below the threshold, the device can use the channel to transmit wireless signals.
To facilitate understanding, identical reference numerals have been used, where possible, to designate identical elements that are common to the figures. It is contemplated that elements disclosed in one embodiment may be beneficially utilized on other embodiments without specific recitation.